The present invention relates to a method of manufacturing a heat exchanger, more precisely relates to a method of manufacturing a heat exchanger for an air conditioner, etc.
A conventional heat exchanging fin 100 is shown in FIG. 9. In a heat exchanger, a plurality of the fins 100 are piled.
The fin 100 is made of a rectangular thin metal plate and includes a plate section 102 and a plurality of collared through-holes 104, which are arranged in the longitudinal direction of the plate section 102. Each of the collared through-holes 104 has a collar 108, which is vertically extended from an edge of a hole section 106, and a flange section 110, which is formed at an upper end of the collar 108. When a plurality of the fins 100 are piled, the flange sections 110 of the fin 100 contact another fin 100, so that the fins 100 can be piled with prescribed separations.
The conventional heat exchanger is manufactured by the steps of: piling a plurality of the fins 100 so as to form a plurality of tube holes 112, each of which is formed by connecting the collared through-holes 104; piercing heat exchanging tubes 114 through the tube holes 112; and inserting expanding bullets 116 into the heat exchanging tubes 114 so as to radially expand the heat exchanging tubes 114 and integrate the heat exchanging tubes 114 with the fins 100 (see FIG. 10).
Transverse sectional shapes of the collars 108 and the heat exchanging tubes 114 are circular shapes. In the conventional method of the heat exchanger, the transverse sectional shapes of the heat exchanging tubes 114 are still circular shapes after the step of expanding the heat exchanging tubes 114.
In the conventional heat exchanger, the circular tubes 114 are integrated with the fins 100. When air is flown, by a fan, in parallel to surfaces of the fins 100, the air is flown perpendicular to the collars 108. Since the transverse sectional shape of the collars 108 are the circular shapes, the air collides with front parts of the collars 108; air turbulent flows (karuman vortex) are generated on rear sides of the collars 108. When frequency of change of pressure, which is caused by the air turbulent flows, coincides with specific oscillation frequency of the heat exchanger, sympathetic vibration is occurred. In the case that drops of dew are formed on surfaces of the heat exchanging tubes 114, the drops of dew are frozen thereon.
To prevent the karuman vortex, heat exchanging tubes, whose transverse sectional shapes are elliptical shapes, are expanded to be integrated with the fins (see Japanese Patent Gazette No. 61-27131). By employing the heat exchanging tubes having the elliptical sectional shapes, the karuman vortex can be reduced and the air can be flown stably.
However, unlike the heat exchanging tubes having the circular sectional shapes, it is difficult to make the heat exchanging tubes having the elliptical sectional shapes, so manufacturing cost of the heat exchanger must be higher.
An object of the present invention is to provide a method of manufacturing a heat exchanger, in which transverse sectional shapes of heat exchanging tubes can be easily formed into elliptical shapes.
The inventors of the present invention have studied and found that the transverse sectional shapes of the heat exchanging tubes and the collared through-holes can be formed into elliptical shapes by inserting expanding bullets, whose transverse sectional shapes are elliptical shapes, into the heat exchanging tubes having the circular transverse sectional shapes.
Namely, the method of the present invention comprises the steps of:
piling a plurality of metallic fins, each of which includes a plurality of collared through-holes, so as to form a plurality of tube holes, each of which is formed by connecting the collared through-holes;
piercing heat exchanging tubes, whose transverse sectional shapes are circular shapes, through the tube holes; and
inserting expanding bullets, whose transverse sectional shapes are elliptical shapes, into the heat exchanging tubes,
whereby the heat exchanging tubes are expanded to have elliptical shapes in transverse sections, and the metallic fins are integrated with the heat exchanging tubes.
In the method, an outer major axis of each of the heat exchanging tubes expanded may be greater than an inner diameter of each of the collared through-holes not expanded, and
an outer minor axis of each of the heat exchanging tubes expanded may be equal to the inner diameter of each of the collared through-holes not expanded. With this structure, deformation of the metallic fins, which is occurred when the heat exchanging tubes are expanded, can be reduced.
In the method, deformation absorbing sections, which are capable of absorbing deformation of the metallic fin, which occurs in the vicinity of the collared through-holes when the heat exchanging tubes are expanded, may be formed in each of the metallic fins. With this structure, the deformation of the metallic fins can be further reduced when the heat exchanging tubes are elliptically expanded. Note that, the deformation absorbing sections may be circular projections, which respectively enclose the collared through-holes and which are formed by bending the metallic fin.
In the present invention, the heat exchanging tubes, whose transverse sectional shapes are the circular shapes, can be expanded to have the elliptical transverse sectional shapes. Therefore, the heat expanding tubes, which previously have the elliptical transverse sectional shapes, are not required. The conventional heat exchanging tubes, which have the circular transverse sectional shapes, can be used.
In the case of using the heat exchanging tubes whose transverse sectional shapes are the elliptical shapes, the heat exchanging tubes must be correctly positioned. Namely, major axes of the elliptical shapes must be arranged in the direction of airflows in the heat exchanger, then the heat exchanging tubes are expanded.
On the other hand, in the present invention, the heat exchanging tubes, which have the circular transverse sectional shapes, are expanded to have the elliptical sectional shapes, so the heat exchanging tubes may be positioned easily. By correctly attaching the expanding bullets, whose transverse sectional shapes are the elliptical shapes, to a tube expanding machine, major axes of the elliptical sectional shapes of the expanded heat exchanging tubes can be easily arranged in the direction of the air flows in the heat exchanger. Therefore, unlike the conventional method, the heat exchanging tubes can be easily pierced through the tube holes and easily expanded. Further, manufacturing cost of the heat exchanger can be reduced.